The objective of the proposed research is to answer several important, currently unexplored questions about the cardiovascular reflex regulation that occurs during static muscular exercise. We have utilized an anesthetized, reflexly intact, canine preparation for initial studies of the circulatory reflex to hindlimb static contractions evoked by stimulation of spinal ventral nerve roots. This basic preparation will be modified as needed and used for the following specific study objectives: a) an assessment of the hemodynamic mechanism responsible for the significant systemic blood pressure elevation in response to static exercise (studies currently underway); b) an assessment of cholinergic and adrenergic effectors in the reflex; the reflex effects on regional vascular beds including resting muscle, skin, kidney, and splanchnic area; the role of central nervous system centers in the reflex; and the interaction of this circulatory reflex with the aorta- carotid baroreceptor and chemoreceptor circulatory reflexes; c) an evaluation of humoral factor(s) in the response to static exercise; and d) a comparative study of the reflex adjustments to static and rhythmic exercise, alone and in combination, in this model.